Reminds me of the swamps in the woods near here. That's some pretty bad BGA you have there. I'd definitely look into your nitrate levels, detritus levels and substrate cleanliness as well...I know I get it from time to time in my 20g tall (miracle grow organic capped with pfs, tons of MTS to churn the sand but still gets funky) when I get lazy...usually if you catch it early you can spot treat it with H2O2. For this though, definitely antibiotics and a blackout. Good luck!